1. Field of the Invention
The invention relates to a heat exchanger assembly for cooling an electronic device.
2. Description of the Prior Art
The operating speed of computers is constantly being improved to create faster computers. With this, comes an increase in heat generation and a need to effectively dissipate that heat.
Heat exchangers and heat sink assemblies have been used that apply natural or forced convection cooling methods to dissipate heat from electronic devices that are highly concentrated heat sources such as microprocessors and computer chips; however, air has a relatively low heat capacity. Thus, liquid-cooled units called LCUs employing a cold plate in conjunction with high heat capacity fluids have been used to remove heat from these types of heat sources. Although, LCUs are satisfactory for moderate heat flux, increasing computing speeds have required more effective heat sink assemblies.
Accordingly, thermosiphon cooling units (TCUs) have been used for cooling electronic devices having a high heat flux. A typical TCU absorbs heat generated by the electronic device by vaporizing a working fluid housed on the boiler plate of the unit. The boiling of the working fluid constitutes a phase change from liquid-to-vapor state and as such the working fluid of the TCU is considered to be a two-phase fluid. Vapor generated during boiling of the working fluid is then transferred to a condenser, where it is liquefied by the process of film condensation over the condensing surface of the TCU. The heat is rejected into ambient air flowing over the condenser and fins are commonly employed on the condenser to increase the heat transferred from the vapor. The condensed liquid is returned back to the boiler plate by gravity and thus the assembly is orientation sensitive.
Due to the universal use of portable or notebook computers which operate in a wide variety of orientations, orientation insensitivity is of growing importance. A few assemblies have been used that can operate in more than merely a horizontal or upright orientation.
Examples of thermosiphon assemblies include U.S. Pat. No. 5,587,880 to Phillips et al. and U.S. Pat. No. 6,840,311 to Ghosh et al.
The Phillips patent discloses an orientation insensitive thermosiphon including a boiling portion and a condensing portion connected by tubes, and a refrigerant which undergoes liquid-to-vapor-to-condensate transformation throughout the evaporator and condenser. The assembly also includes an electric heater which operates when the assembly is in an upside down position in order to create frothing of the condensate in the tubes directly below the condensing portion to bring the liquid refrigerant back up to the boiling portion without the use of gravity by way of bubbles.
The Ghosh patent teaches an orientation sensitive thermosiphon assembly comprising a housing defining a boiling chamber and having a first condensing tube extending in one direction from the boiling chamber and a second condensing tube extending in an opposite direction wherein both condensing tubes extend upwardly.
Although the prior art effectively dissipates heat from electronic devices, there is a continuing need for alternative designs for effectively dissipating heat from electronic devices. Specifically, there is a need for alternative designs for orientation insensitive thermosiphons that can operate in more orientation than conventional orientation insensitive thermosiphons, including an upside down position, without the use of electronic controls, pumps, or electric heaters.